Induction heating is a well-known surface hardening process that has been widely used by the metallurgical industry to heat treat metallic work pieces. Its generally superior controllability makes it an attractive alternative to previous surface hardening techniques.
Induction heating is typically achieved by passing a high frequency current through a suitably shaped inductor. For example, inductors have been designed to include a substantially circular internal void for the heating of work pieces having a substantially rounded or circular cross-section, such as cammed work pieces including cam members and the like. The inductor is then typically positioned in close proximity to the surface to be hardened. The rapid current reversal induces eddy currents in the surface causing it to heat above the hardening (e.g., austenitizing) temperature.
Austenitizing generally involves heating of the work piece above its transformation temperature and then quenching it in a salt bath or other quenching medium (e.g., oil, water, air, and/or the like) in order to extract the heat at a sufficiently high enough rate to prevent the formation of undesirable high-temperature-transformation qualities on its surface or in its microstructure.
Towards this end, the inductor is used to heat the work piece with a subsequent spray quench so as to achieve the rapid heating and cooling which results in hardening. This process is extremely versatile and can be used on a variety of metallic work pieces possessing different shapes and sizes.
With respect to work pieces that have a generally rounded or cammed cross-section, there has been some difficulty in uniformly heating the external surfaces thereof due, in part, to the irregular shapes of these cammed work pieces. Cammed work pieces typically have a lobe portion (having a substantially ovoid appearance) and a spaced and opposed heel portion (having a substantially circular appearance). When subjected to conventional induction heating processes, the lobe portion has a tendency to overheat, thus resulting in poor overall surface hardening results.
In an effort to overcome this problem, several approaches were attempted, none of which produced acceptable results.
With respect to FIGS. 1-2, an induction heating system 10 is shown including a locator system 12, an inductor system 14, and a work piece 16, in accordance with the prior art. The dashed lines indicate a quenching system Q for controlled cooling of the work piece 16.
The locator system 12 supports the work piece 16 during the heat-treating process. Additionally, the locator system 12 includes a rotation system 18 that can selectively rotate the work piece 16, if desired. The locator system 12 includes a central axis A.
In this system 10, the work piece 16, e.g., a cam member, includes a lobe portion L and a heal portion H. Formed along the central axis AA of the work piece 16 is an area defined as a void 20. It should be noted that the central axis AA is slightly offset from the geometric axis of the work piece 16. However, the central axis A of the locator system 12 substantially concentrically aligns with the central axis AA of the work piece 16.
The inductor system 14 includes an inductor 22. Formed along the central axis AAA of the inductor 22 is an area defined as a void 24. It should be noted that the central axis AAA is substantially aligned with the geometric axis of the inductor 22. Additionally, the central axis AAA of the void 24 of the inductor 22 substantially concentrically aligns with both the central axis A of the locator system 12 and the central axis AA of the void 20 of the work piece 16.
The inductor 22 typically includes an area known as a split region 26 (also referred to as a “fish-tail” region) where in conventional induction heating systems there is a distortion of the electromagnetic field due to a current cancellation phenomenon. As a result of this phenomenon, a soft spot or “necking” of the hardening pattern could appear in the heated work piece 16.
As can be clearly seen in FIGS. 1-2, in the initial fixtured position shown, the distance D1 between the external surface 28 of the heel portion H from the internal surface 30 of the inductor 22 is substantially greater than the distance D2 between the lobe portion L and the internal surface 30 of the inductor 22. Thus, even if the work piece 16 were to be rotated during the heat-treating process, there would most likely be uneven heating of the external surface of the work piece 16 possibly resulting in an uneven hardening pattern.
Another approach to this problem is shown in FIGS. 3-4. An alternate induction heating system 100 is shown, in accordance with the prior art. As with the induction heating system 10 shown in FIGS. 1-2, the system 100 includes a locator system 112, an inductor system 114, and a work piece 116. The dashed lines indicate a quenching system Q for controlled cooling of the work piece 116. However, there is no provision for rotating the work piece 116 relative to either the locator system 112 or the inductor system 114.
As with the previously described system 10, the central axes A, M, and AAA of the locator system 112, the void 120 of the work piece 116, and the void 122 of the inductor 222, respectively, are substantially concentrically aligned.
This system 110 relies on fixturing the work piece 116 is a stationary position on the locator system 112 (i.e., the work piece 116 does not rotate with respect to the inductor system 114), with the lobe portion L of the work piece 116 oriented towards the split region 126 of the inductor 122. The distance D3 between the external surface 128 of the heel portion H and the internal surface 130 of the inductor 122 is substantially greater than the distance D4 between the lobe portion L and the internal surface 130 of the inductor 122. However, because the lobe portion L is oriented towards the split region 126, it is highly likely that a necking effect will be observed, thus resulting in uneven hardening of the surface of the work piece 116, especially in the area of the lobe portion L.
Therefore, there exists a need for an apparatus and method of using the same that permits substantially uniform induction heating of a work piece, especially a metallic work piece having irregular and/or non-linear surface characteristics, such as cammed surfaces, including those cammed surfaces having a lobe portion and a heel portion, such as a cam member, to be used in conjunction with a camshaft, for example.